Autoinjector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc.
Autoinjectors require some form of energy input in order to operate. Typically this is achieved by the user performing a “priming” or “cocking” action prior to the injection. This may make the device more complicated to use, as it increases the number of user steps. Also, the actions required, for example pulling, pushing or twisting to charge a spring, may be difficult for a user to perform, particularly if the user is elderly or has dexterity problems.
However, two main user risks have been identified with such a device. Firstly, the user might press a trigger button several times or hold on to the trigger button for too long, causing multiple doses to be injected. Secondly, there would be a risk of the device being triggered accidentally.
In WO 02/47746 A1 a device for auto-injection of a dose of medicament is disclosed, comprising a housing arranged to contain a medicament container therein and comprising a contact part intended to be applied against an injection site, a needle cover surrounding a needle arranged to the medicament container and extending at least the length of the needle, spring means capable of, upon activation, pushing the needle past the end of the needle cover as well as operating said medicament container to supply the dose of medicament, first locking means capable of locking said spring means in a pressurised state, first activating means capable of, upon manual operation, releasing said spring means for injection, characterised by a second locking means capable of locking said first activating means and a second activating means, capable of releasing said second locking means when said contact part is exposed to pressure.
WO 2006/130098 A1 discloses a device for delivery of predetermined doses of liquid medicament. The device comprises a servo drive spring acting in the way of a clock spring for generating a torque. The torque is used for rotating a drum which advances a threaded plunger rod. The rotation of the drum may be blocked by a pin engaging with a slot when a dose of medicament has been delivered.
U.S. Pat. No. 6,972,007 B2 discloses a device for administering an injectable product in doses, the device comprising a dosing member connected to a locking means, which may be held in latching positions thus taking off a spring force onto a driven member which serves for advancing a piston and consequently for delivering a set dose of medicament. The locking means is held in the locking position by grooves engaging with corresponding protrusions.
WO 2006/045529 A1 discloses an injection device having a helical spring adapted to provide a force in the axial direction of the injection device for ejecting a dose of medicament. A rotary movement of a dose indicator barrel is caused by the force of the resilient member acting on a thread. The rotational movement may be manually blocked by appropriately switching a locking member between a locking state and an unlocking state.
WO 2007/063342 A1 discloses a pen-type injector for receiving a medication container. The injector comprises a housing and a torsion spring coupled to a drive member. A dose setting knob is coupled to the spring and rotatably coupled to a housing such that rotation of the knob in a first direction results in compression or twisting of the spring. A user actuable button is coupled to the housing for axial motion relative thereto, the button being coupled to the torsion spring to unwind or expand in discrete steps with each press of the button, which is achieved by engaging teeth of sprung legs of a clutch collet with a toothed rack.